1. Technical Field
The present invention relates to an electronic exchange, and more particularly to a tone supplying device for generating several kinds of tone signals which an exchange can provide for public subscribers.
2. Related Art
Generally, a tone supplying device, which is mounted in an exchange, is constructed of a board-type generating dial tone, ring back tone, hold tone, busy tone, trunk line busy tone, warning tone, immediate ring back tone, howling tone, etc.
As described in more detail below, up to this point, tone generators for an electronic exchange have a microprocessor which generates overall control signals and which reads several kinds of tone signals typically stored in a tone memory so as to supply them to a PCM highway. However, in such systems, there has been a drawback in that the tone supplying device has had to operate under the control of the microprocessor, and thus peripheral circuits have been indispensable for the operation of the tone supplying device. This has tended to unnecessarily increase the production cost in the manufacture of such tone generators for electronic exchanges.
The following patents are considered to be representative of the prior art relative to the present invention, but are burdened by the disadvantage discussed above: U.S. Pat. No. 5,666,357 to Jangi, entitled DTMF Tone PasserIn A Voice Communication System, U.S. Pat. No. 5,530,743 to Sakurai, entitled Telephone Exchange Apparatus And Tone Sending Method In Telephone Exchange Apparatus, U.S. Pat. No. 4,907,262 to Kwun, entitled Method Of Transmitting Dual Tone Multi-Frequency During Communication In A Private Branch Exchange Using Keyphones, U.S. Pat. No. 4,695,804 to Bardl et al., entitled Apparatus For Generating A Multi-Frequency Signal, U.S. Pat. No. 4,639,554 to Masuda et al., entitled Dual-Tone Multiple-Frequency-Signal Generating Apparatus, U.S. Pat. No. 4,571,723 to Lusignan et al., entitled Pulse Code Modulated Digital Telephony Tone Generator, U.S. Pat. No. 4,541,088 to Sarson, entitled Tone Generation Circuit For Automatic PCMK-TDM Telecommunication Exchange, U.S. Pat. No. 4,393,740 to Niezgoda et aL, entitled Programmable Tone Generator, U.S. Pat. No. 4,390,754 to Holberg, entitled Tone Generator Circuit, U.S. Pat. No. 4,070,942 to Aoki, entitled tone Generator, U.S. Pat. No. 4,056,692 to Place, entitled Digital Tone Generator, and U.S. Pat. No. 3,959,604 to Newsom et al., entitled Digital Calling Signal tone Generating Circuitry. 
It is, therefore, an object of the present invention to provide a device for supplying a desired tone using a simple counter without employing a high-priced microprocessor in the design of a tone supplying device.
This and other objects of the present invention are attained by providing a tone supplying device for an exchange with a plurality of tone tables for storing a predetermined magnitude of successive tone signals not having a predetermined intermittence ratio in a table form therein, the tone tables being composed of a great number of tone tables depending on the type of tone signal; a cadence table for generating cadence data intermitting the output of the plurality of tone tables including the predetermined magnitude of successive tone signals in a table form; a first counter for allowing the counted output to be divided into more significant bits and less significant bits, and allowing the counting output of the more significant bits to be supplied as an address signal to the plurality of tone tables to enable them, and allowing the less significant bits to be supplied to the plurality of tone tables and the cadence table simultaneously, thereby to output a counting signal so as to generate a tone selecting signal for intermitting a corresponding successive tone signal and the predetermined magnitude of successive tone signals; a second counter for generating an address signal which is a reference of cadence in a regular period, and for supplying the address signal to the cadence table; a plurality of buffers for receiving the successive tone signals outputted each from the plurality of tone tables and storing them therein, and allowing a cadence signal outputted from the cadence table to intermit the stored successive tone signals to output them.